Materials of this type, especially in the form of thin films, can be used as devices for data storage. A typical example is a liquid crystal polymer which will usually scatter light when being cooled slowly down from the isotropic to the mesogenic state (see, for example, V. P. Shibaev et al., Thermo-Recording on the Liquid Crystalline Polymers, ed. by A. Blumstein, New York, 1985, pp. 345-350); scattering is due to fluctuations of the direction of the mesogenic groups on a sub-micron to micron scale.
When the glass transition temperature is not too much lower than the clearing temperature of the liquid crystal polymer, rapid cooling from the isotropic state below the glass transition state will result in a transparent glassy state, i.e. the isotropic structure of the liquid crystal polymer is frozen in (see, for example, H. Fimkelmann, Phil. Trans. R. Soc. Lond. A309 (1983), 105).
The film can therefore be used as permanent data storage: the information is written in by heating with a suitable heat source, for example by a laser beam, with subsequent supercooling and is depicted in transparent Symbols on a scattering background. Permanent data storage, however, requires that the storage temperature is lower than TG, otherwise the film will be transferred to the scattering state again.
It is evident from this that the liquid crystal polymer must exhibit the following features when being used as permanent data storage:
Up to now, however, it was not possible to design a liquid crystal polymer exhibiting all these properties. In particular, the present inventors found out that low-T.sub.G liquid polymers (T.sub.G &lt;50.degree. C.) when being solved in a solvent like dichloromethane (DCM) or toluene and cast as a thin film on a surface with subsequent evaporation of the solvent, quite generally scatter light well; contrary to this, high-T.sub.G (T.sub.G &gt;70.degree.-80.degree. C.) liquid crystal polymer films generally exhibit a completely insufficient scattering power or do not scatter at all. This is an experimental fact which up to now could not be satisfactorily explained theoretically.
It was therefore necessary to develop a completely new material concept in order to fulfill the requirements outlined above and to fulfill them to a greater extent than is the case with conventional liquid crystal polymers. Other objects of the present invention are evident for the expert from the following detailed description of the invention.
It was found that these objects can be achieved by the polymeric composite materials according to the present invention.